More high schools across Minnesota and the nation are starting later each morning — a move that could help teens not just in the classroom, but also on the road.

Findings of a University of Minnesota study released Wednesday are the first to conclusively link later morning school starts to higher test scores, better grades and fewer teen car crashes.

The latest study puts weight behind an issue hotly debated by parents, students and school leaders nationwide.

“People keep asking me, ‘Is this [later school start times] really making a difference?’ ” said project director Kyla Wahl­strom, a former North St. Paul principal who’s studied school start times for 17 years. “We didn’t have the proof until now.”

For three years, researchers at the university’s Center for Applied Research and Educational Improvement analyzed data from more than 9,000 students at eight high schools in Minnesota, Colorado and Wyoming. Overall results showed a boost in attendance, test scores and grades in math, English, science and social studies for schools that shifted the school day later into the morning.

Schools also saw a decrease in tardiness, substance abuse and symptoms of depression. Some even had a dramatic drop in teen car crashes.

“The eight hours of sleep seems to be a tipping point for making healthy or unhealthy behavioral decisions,” Wahlstrom said.

But, the study found, only 34 percent of students are getting the recommended eight hours of sleep when school starts at 7:30 a.m. compared with 66 percent of students getting eight hours of sleep at schools that start as late as 8:55 a.m.

The study, funded by a $300,000 grant from the Centers for Disease Control and Prevention in Atlanta, reaffirms what experts and school leaders have long suspected about better syncing school schedules to teen sleep patterns.

“There’s really no downside in terms of outcomes for kids,” Wahlstrom said.

Parents approve

The findings are catching the attention of schools nationwide, including Minnesota school leaders at Alexandria’s high school, which just approved a later, 8:25 a.m. start next school year.

Years ago, Edina and Minneapolis high schools were among the first to make the change.

“A well-rested student body is a good, productive student body,” Edina High School Principal Bruce Locklear said, adding that it would be difficult to revert to the earlier time. “It’s a culture thing; the students believe in it and embrace it.”

Parent Leanne Montgomery said the high school’s 8:25 a.m. start worked better for her daughter before she graduated, while others, like her son, a sophomore, prefer an optional earlier arrival at 7:25 a.m. to take extra advanced classes.

“It’s not for everybody; some just need to sleep,” she said. “But for others, their internal clocks are different.”

When Edina initially made the switch from a 7:20 a.m. start, some parents worried about the impact on busing, sports and child care. But according to another of Wahlstrom’s previous studies, after one year, 92 percent of Edina parents surveyed preferred the later time. She also analyzed Minneapolis high schools’ move from 7:15 a.m. to 8:40 a.m., finding a decrease in dropout rates and students’ depression and an increase in grades.

More rested, less rushed

Not all schools have seen measurable benefits from starting later.

St. Louis Park High School, which was included in the U’s latest study, didn’t have conclusive academic results. Still, when Superintendent Rob Metz was principal, he remembers greeting students at 7:15 a.m. who were barely awake. Now, with an 8:20 a.m. start, he said teens are more rested and not as rushed.

The other metro schools in the study — Mahtomedi High School, Woodbury High School, Park High School and East Ridge High School — did see benefits such as Mahtomedi’s significant increases in ACT test scores and attendance after moving from a 7:30 a.m. start time to 8 a.m. Plus, the number of student vehicle crashes dropped 65 percent, based on state data of drivers 16 to 18 years old.

Another school in the study, Jackson Hole High School in Wyoming, had a 70 percent drop in the number of teen crashes after the school switched from a 7:35 a.m. start time to 8:55 a.m. — the latest of all eight schools in the study.

“It makes sense, because kids who are sleep-deprived, like most people who are sleep-deprived, are more distracted,” Wahlstrom said.

She cautions that the study doesn’t prescribe later high school start times and she hopes to continue to study crash data. But with more high schools in Minnesota and across the country turning start clocks forward, she hopes the new findings help schools make a decision themselves.

“Schools are really complex, bureaucratic places and to make a shift like this is changing the norms of a community,” she said. “I’m not saying this is a magic bullet, but clearly the more we’re learning about teens and sleep, the more we can make good choices.”